refactor: Deduplicate env var

[koooge]

Hi there, telegraf-ds's daemonset has the duplicated env var HOSTIP.

...
      containers:
      - env:
        - name: HOSTIP
          valueFrom:
            fieldRef:
              apiVersion: v1
              fieldPath: status.hostIP
        - name: HOSTNAME
          valueFrom:
            fieldRef:
              apiVersion: v1
              fieldPath: spec.nodeName
        - name: HOSTIP
          valueFrom:
            fieldRef:
              apiVersion: v1
              fieldPath: status.hostIP
...